1. Field of the Invention
This invention pertains generally to circuit interrupters and, more particularly, to circuit interrupters, such as, for example, medium voltage vacuum circuit breakers, employing one or more poles each of which includes a vacuum interrupter. The invention also pertains to operating mechanism assemblies for vacuum circuit interrupters.
2. Background Information
Circuit interrupters provide protection for electrical systems from electrical fault conditions such as, for example, current overloads, short circuits and abnormal level voltage conditions. Typically, circuit interrupters include a spring powered operating mechanism which opens electrical contacts to interrupt the current through the conductors of an electrical system in response to abnormal conditions, although a wide range of driving mechanisms may be employed.
Circuit interrupters, such as, for example, power circuit breakers for systems operating above about 1,000 volts typically utilize vacuum interrupters as the switching devices. Vacuum switching devices (e.g., circuit interrupters; circuit breakers; switches; reclosers) include separable main contacts disposed within an insulating housing. Generally, one of the contacts is fixed relative to both the housing and to an external electrical conductor which is interconnected with the circuit to be controlled by the circuit interrupter. The other contact is moveable. In the case of a vacuum circuit interrupter, the moveable contact assembly usually comprises a stem of circular cross-section having the contact at one end enclosed within a vacuum chamber and a driving mechanism at the other end which is external to the vacuum chamber. An operating rod assembly comprising a push rod, which is fastened to the end of the stem opposite the moveable contact, and a driving mechanism provide the motive force to move the moveable contact into or out of engagement with the fixed contact.
Vacuum interrupters are typically used, for instance, to reliably interrupt medium voltage alternating current (AC) currents and, also, high voltage AC currents of several thousands of amperes or more. Typically, one vacuum interrupter is provided for each phase of a multi-phase circuit and the vacuum interrupters for the several phases are actuated simultaneously by a common operating mechanism, or separately by separate operating mechanisms (and auxiliary switches).
Known medium voltage vacuum circuit interrupters using spring-charged stored energy mechanisms lack the requisite force to maintain necessary contact pressure to withstand current levels dictated by a withstand test for a 75 kA rating.
Accordingly, there is room for improvement in circuit interrupters. There is also room for improvement in operating mechanism assemblies for vacuum circuit interrupters.